260 THE INCOME OF ENERGY 



has fasted at least fourteen days. After about 

 twenty-four hours, remove the intestine and im- 

 merse it from thirty to forty minutes in 0.25 per 

 cent osmic acid solution. 1 



Slice the epithelial layer from its base. Tease 

 on a glass slide and examine under the micro- 

 scope. 



Particles of fat stained deep-brown by the osmic 

 acid will be found in the epithelial cells. 



In a " control " frog that has fasted fourteen 

 days, show that the intestinal epithelium is free 

 from fat. 



2. Open the stomach of a frog the brain and 

 spinal cord of which have been destroyed. Tie 

 a glass cannula in the pylorus. Tie a ligature 

 around the lower end of the intestine. Remove 

 the intestine. Place about 1 c.c. normal saline 

 solution in a test-tube. Hang the intestine in 

 the test-tube by passing the cannula through 

 the cork. Place a little neutral olive oil in the 

 intestine. After about twenty-four hours stain 

 the epithelium with osmic acid and examine as 

 before. 



Drops of fat will be found in the cells, but the 



1 Preparation of Osmic Acid Solution. The glass capsule 

 containing a known quantity of osmic acid is placed in a bottle 

 and enough water is then added to make the required solution. 

 The capsule is then broken. [The vapor of osmic acid is very 

 irritating.] 



